The association of shift work and nitrous oxide exposure in pregnancy withbirth weight and gestational age

We examined the relation between shift work and occupational nitrous oxide exposure in the second trimester of pregnancy and birth weight and gestatio nal age at delivery among the members of the Swedish Midwives Association. Eighty-four per cent of members who were registered in 1989 responded to a postal questionnaire concerning occupational exposures, including work sche dule and the use of nitrous oxide, in relation to each of their pregnancies . We obtained information on births from the Swedish Medical Birth Register . We used models with allowance for dependence between births for the same woman and found that: night work was associated with preterm birth (<37 wee ks) [odds ratio (OR) = 5.6; 95% confidence limits (CL) = 1.9, 16.4] and to a lesser extent with low birth weight [OR = 1.9 (95% CL = 0.6, 5.8)]. Three -shift work schedule (day, evening, and night rotation) showed a possible a ssociation with preterm birth [OR = 2.3 (95% CL = 0.7, 7.3)]. Exposure to n itrous oxide use was associated with reduced birth weight (-77 gm; 95% CL = -129, -24) and an increase in the odds of infants being small for gestatio nal age (less than or equal to 10th percentile of weight for gestational we ek) (OR = 1.8; 95% CL = 1.1, 2.8).